As for the garbled gfx, that's actually a bug in the game: it doesn't initialize the decimal flag. You won't see this if you just load the game from the harmony menu (as the menu itself clears the D flag), but it might happen randomly when putting the game on a real cart.
Yes, it does not clears decimal flag at game initialization, I'm aware this bug by long time...
This was one of my firsts game ever, I was learning not only how to code for 2600 and also trying to understand 6502 assembly.
Decimal flag seems to start at 0 most of times when you power on the console, but at very random event it could start at 1 and then I got problems.
I not sure if I fixed it on last revisions (there was like 3 game revisions, the ROM was not released to the public).
I only noticed this glitch on my hardware like 2 times ever, and I thought was a cartridge connection problem, which was solved by re-inserting the cart (actually power cycling the console fix it).
The lasts Stella emulator versions, in order to perfect the emulation, is randomizing the processor flags, so this bug now happens more often.
The game also have others small glitches that really annoys me, sorry about that.
Anyway, after 11 years, have one of you guys found the game's Easter Egg?